Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

117
FXUS65 KTFX 301150
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
450 AM MST Thu Jan 30 2025

Aviation Section Updated.

.KEY MESSAGES...

- Cold morning temperatures continue in valleys of Southwest MT
  for another night.

- Mostly quiet conditions today will give way to a more stormy
  weather weather pattern from Friday thru next Thu.

- Another round of strong winds possible Friday night into
  Saturday in the Browning and Cut Bank areas.

- Snow develops along the divide on Friday, and then spreads
  eastward over the weekend, the snow lasting much of next week.

- Mild temperatures over North Central MT will return to more
  February like over the weekend and for much of next week.

&&

.DISCUSSION...
/Issued 257 AM MST Thu Jan 30 2025/

 - Meteorological Overview:
The overall mostly quiet weather pattern that has resided over
the CWA over the past few days with an upper level ridge to our
west is beginning to slowly break down. The next upper level trof
is progged to move into Montana by Saturday, but strong winds are
possible ahead of the trof Friday night into Saturday in the
Browning/Cut Bank areas. Mid level winds are progged near 65
knots, combined with weak short waves moving through, the stronger
mid level winds will mix down at times. Thus a high wind watch
was issued for this region. As the upper level trof also
approaches, snow will develop right near the divide. The snow
could be heavy at times over northern Beaverhead County, along
with the Rocky Mountain Front from Friday thru Saturday night.
Thus the winter storm watch was changed to a winter storm warning
for these areas. Lighter snowfall develops Friday night into
Saturday along the MT/ID border near West Yellowstone, thus a
winter weather advisory was issued for this portion of the CWA.

On Saturday night, a Canadian cold front will move southward
through North Central MT. This cold front will likely stall out
along the I-90 corridor from Butte to Bozeman on Sunday. The flow
aloft will become more westerly by Sunday, allowing for
overrunning snowfall to develop over much of Central and
Southwest MT. The forecast models do differ on how much/long the
overrunning will last. Thus some models have little snowfall and
some have quite a bit. With probabilities near 50 percent, a
winter storm watch was issued from 12z Sun to 00z Tue for mostly
the mountain areas across much of the CWA, (the exception being
the Bears Paw Mountains where the snowfall is expected to be
lighter.) With the potential for overrunning continuing through
much of Tue/Wed/Thu...additional snow accumulations are expected
each day through most of next week.

Again, colder air will move southward, generally starting on
Sunday. This cold air mass will likely not be quite as cold as
previous cold snaps, but still cold enough that some cold air
advisory statements might be needed at times over North Central
MT, especially for areas along/north of Highway 2 from East
Glacier Park to Harlem. Ironically, the cold air from this system
is expected to stay out of the valleys south of I-90 from Butte
to Bozeman, so overnight lows in that region will generally just
be seasonably cold.

 - Forecast Confidence & Scenarios:

There is the potential for strong winds late Friday into Saturday
in the Browning/Cut Bank areas. The latest probabilities for
strong winds have increased a bit, to near 75 percent chance for
wind gusts over 60 mph.

For snowfall, it is looking like two separate weather systems
will be causing the snowfall over the weekend and into early next
week. The first snowfall event will occur with the upper level
trof approaching, and this snowfall will be focused for areas
along the divide. There is an 80 percent chance snowfall could
exceed 6 inches for locations right near the divide, including
Marias Pass over the weekend.

There looks to be enough of a break between weather systems, that
a second weather system looks to develop later on Sunday, and
then continue through late next week. This is the weather system
that models differ on how much/where any heavy snowfall could
fall. It is mostly because of an overrunning situation. Thus
confidence is not quite as high right now, especially with some
models having lighter snowfall, thus a winter storm watch was
issued for many mountain areas from Sunday through Monday.
Overall, light accumulating snowfall is expected across much of
the CWA through most of next week, but the probabilities for 6
inches or more of snowfall are on the low side generally less
than 40 percent in the mountains and less than 10 percent at the
bigger cities at lower elevations. Brusda

&&

.AVIATION...
30/12Z TAF Period

VFR conditions will generally continue over North Central,
Central, and Southwest Montana through at least 31/12Z, as a
westerly flow aloft moves mainly high-level cloudiness over the
area. However, valley inversions with light winds may allow
periods of haze to form at the KHLN and KBZN terminals, but
visibility reduction is only expected to be down to 5SM at times,
which may cause some terrain-obscuration.

Winds will be a bit more of a concern over the area, as the
moderate westerly flow aloft will cause some mountain wave
turbulence, as well as some low-level wind shear over the plains.
Wind gusts there will mostly be in the 20 to 30 kt range, mainly
through 03Z or so. However, gusts of 35 to 45 kt are expected to
persist through around 21Z or so from KCTB west to the Rockies,
then decrease after then. -Coulston

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  33  43  34 /   0   0   0   0
CTB  48  26  39  29 /   0   0   0  10
HLN  31  14  41  27 /   0   0   0  20
BZN  34  11  38  23 /   0   0   0  20
WYS  34  -1  28  17 /   0   0  20  90
DLN  38  17  36  21 /   0   0   0  20
HVR  43  23  36  26 /   0  10  10  10
LWT  41  27  41  29 /   0   0   0  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 8 AM Friday to 5 AM MST Sunday for
East Glacier Park Region-Southern Rocky Mountain Front.

High Wind Watch from Friday evening through Saturday evening for
Eastern Glacier, Western Toole, and Central Pondera-Northern
High Plains.

Winter Storm Watch from late Saturday night through Monday
afternoon for Big Belt, Bridger and Castle Mountains-East
Glacier Park Region-Elkhorn and Boulder Mountains-Gallatin and
Madison County Mountains and Centennial Mountains-Little Belt
and Highwood Mountains-Northwest Beaverhead County-Snowy and
Judith Mountains-Southern Rocky Mountain Front-Upper Blackfoot
and MacDonald Pass.

Winter Weather Advisory from 5 PM Friday to 5 AM MST Sunday for
Gallatin and Madison County Mountains and Centennial Mountains.

Winter Storm Warning from 8 PM Friday to 5 AM MST Sunday for
Northwest Beaverhead County.

&&

$$
http://www.weather.gov/greatfalls